Technical Field
This disclosure relates to clutches or clutch modules for manual transmissions of automobiles that facilitate synchronization of the rotational speed of the selected gear with the rotational speed of the transmission shaft.
Description of the Related Art
An internal combustion engine of an automobile generates power in the form of reciprocating motion of its pistons. The crankshaft converts this reciprocal motion into rotary motion. The rotary motion of the crankshaft, however, is not transmitted directly to the driving wheels or to the drivetrain because the crankshaft rotates at high rotational speeds, which are inappropriate for starting, stopping and normal travel. Specifically, automobile engines typically operate over a range of about 600 to about 7000 rpm, while the wheels rotate between 0 rpm and about 1800 rpm. It is the function of the transmission to convert the high rotational speed of the crankshaft to a slower wheel speed and to increase torque in the process. While both manual and automatic transmissions provide the same basic functions of speed reduction and torque increase, this disclosure relates to manual transmissions.
Instead of connecting directly to the transmission, the crankshaft connects to a flywheel, which connects to a transmission input shaft, sometimes referred to as a mainshaft. In one example, the transmission selectively couples the input shaft through two gear sets, each providing a gear ratio, and eventually to an output shaft, sometimes referred to as the driveshaft. In many designs, the input shaft fixedly connects to an input pinion that meshes with an input gear fixedly connected to a parallel counter shaft. Thus, the counter shaft rotates with the input shaft, but at a somewhat lower speed to the gear ratio provided by the input pinion and the input gear of the counter shaft. The counter shaft also fixedly connects to a plurality of gears, typically numbered from one to four, five or six. Each of these numbered gears, which rotate with the counter shaft, also mesh with and form gear sets with like-numbered gears through which an output shaft passes. The numbered gears of the output shaft do not connect to the output shaft, but instead ride on bearings. Each pair of enmeshed numbered gears, one on the counter shaft and one on the output shaft, form a gear set and provide a gear ratio. Because the output shaft is not fixedly connected to the numbered gears through which it passes, the transmission also includes a plurality of clutches or clutch modules that selectively couple the output shaft to one of these numbered gears and therefore to one of the gear sets.
Manual transmissions are available in a variety of different designs and clutch modules may be required to connect gear sets to an input shaft, one or more counter shafts or an output shaft. Hence, use of the term “transmission shaft” below may refer to any shaft of a transmission that may be selectively coupled to a gear set by a clutch module.
Before a transmission shaft connects to one of the gears through which it passes, or before a gear shift takes place, it is preferable to have the selected gear rotating at or about the same speed as the transmission shaft to which it will be coupled. This process is known as synchronization. Modern manual transmissions include various means for achieving synchronization of the transmission shaft with the selected gear, or the gear set being shifted to, so the transmission shaft and the selected gear rotate at about the same rotational velocity when the shift takes place. Synchronization may be achieved with synchronizing rings, as disclosed initially in U.S. Pat. No. 2,579,090 and later in U.S. Pat. No. 3,688,883. As shown in U.S. Pat. No. 3,688,883, a synchronization ring may couple to the selected gear or to a clutch body mounted to the selected gear. As gear shifting commences, a shift sleeve, which rotates with the transmission shaft, moves into frictional engagement with the synchronization ring before clutch teeth of the shift sleeve engage clutch teeth of the selected gear. The frictional engagement between the shift sleeve and the synchronization ring imparts rotation to the selected gear. As a result, the transmission shaft (and shift sleeve) and the selected gear rotate at or about the same rotational speed before the shift to the selected gear, or the selected gear set, is completed. Synchronizing rings typically include a conical friction surface, which engages a corresponding conical surface on the selected gear (or clutch body connected to the selected gear). The resulting frictional engagement between the synchronizing ring and the selected gear establishes the desired synchronization between the transmission shaft and the selected gear.
Clutch modules that perform synchronization as well as gear shifting can be complex in design, difficult to assemble and therefore costly to produce. Further, as noted above, multiple clutch modules may be required. Accordingly, a need exists for improved clutch and synchronization modules that are easy to assemble, reliable and cost efficient to produce.